Communications networks typically include a number of interconnected communicating nodes. The connections between nodes are usually made through physical wires or optical links. Wireless networks, in which nodes connect through wireless links, are also well known.
Wireless networks generally employ radio-frequency channels to communicate between nodes. In a wireless network that uses Frequency Division Multiple Access (FDMA), channels are defined by the use of one or more radio-frequencies. For example, node A may communicate with node B on one channel using frequency 1, while node C may communicate with node D on another channel using frequency 2.
In a wireless network that employs Code Division Multiple Access (CDMA), channels are defined by a set of spreading codes (a spreading code may control, or allow variations in, transmission frequencies in accordance with prescribed mathematical function or functions). Thus, for example, node E may transmit to node F using a first spreading code and node G may transmit to node H using a second spreading code. The two transmissions may overlap in frequency and time. On reception, nodes F and H can extract the intended information using the first and second spreading codes, respectively.
In a wireless network that employs Time Division Multiple Access (TDMA) channels, one or more time slots may be assigned to each node, such that each respective node may transmit information only within its assigned time slots. FIG. 1 illustrates an exemplary wireless network 100 that employs TDMA to define multiple channels.
Wireless network 100 includes nodes 102-112. Nodes 102-112 may be included in, for example, an airplane, a ground station, a sensor, and a vehicle, such as a car or a ship. Each node may be assigned a timeslot in which to transmit. For example, node 102 is assigned timeslot 116, node 104 is assigned time slot 122, node 106 is assigned timeslot 114, node 108 is assigned timeslot 118, node 110 is assigned timeslot 120, and node 112 is assigned timeslot 124. Thus, each node may transmit to other nodes only during the node's respective assigned timeslots. A receiving node may thus receive information from another transmitting node when the transmitting node transmits during its assigned timeslot.
Typically, each node in a network has a single transceiver. Usually the single transceiver may transmit or receive, but may not simultaneously transmit and receive because the power used to transmit information may interfere with reception. Such transceivers are called half-duplex transceivers. Full-duplex transceivers are capable of simultaneous transmission and reception. This can be achieved by devoting one frequency (in an FDMA network) or one spreading code (in a CDMA network, direct sequence spread spectrum radios, or frequency hopping radios) to transmission in one channel and another frequency or spreading code to reception in another channel. Thus, a full-duplex transceiver actually transmits and receives simultaneously by using two channels.
Some nodes in wireless networks have multiple transceivers that are operated independently of other transceivers. In some relatively rare cases multiple transceivers may be used in a coordinated fashion within a given network node. For example, in one system, a node may transmit and receive distinct synchronization patterns on multiple channels in parallel using closely coordinated multiple transceivers.
Due to increasing demand for more bandwidth within communications networks, a more efficient way of transmitting and receiving information among nodes in a wireless network is desired.